The invention relates to a device for adjusting an article of furniture, which includes the following: at least one drive assembly having a DC positioning motor, which is connected to a mains power source; a control unit with switching means operating the at least one positioning motor; and a mains-disconnect relay connected in series with a plug assembly or a supply line connected to the mains power source.
Adjustment devices for adjusting an article of furniture of the afore-described type are disclosed, for example, in EP 0 615 667 B. The mains power of the adjustment device described in this reference is disconnected according to the operating principle disclosed in DE 21 05 570 and has proven to be effective in practice. The device, however, could benefit from improvements relating to the following effect. Since a single pushbutton switch is used to operate the mains-disconnect relay as well as a relay for controlling the positioning motor, i.e., two switching operations are activated by a single pushbutton switch, there exists the risk that when the pushbutton switch is pressed accidentallyxe2x80x94for example when the control unit is activated unintentionally during sleepxe2x80x94the article of furniture can be moved unintentionally. This situation must be reliably preventedxe2x80x94for example, when adjustments are made on hospital beds. When the switching assembly is designed as a pushbutton switch, operating the positioning motors becomes particularly simple. However, since the pushbutton switch can easily be activated unintentionally, the problem may arise that the mains power is also unintentionally applied.
It would therefore be desirable to provide an adjustment device for an article of furniture that eliminates the afore-described disadvantages and simultaneously improves the safety of the device.
According to one aspect of the invention, a simple switching means, which is separate from the switching means (or switching assembly) of the control unit for actuating the at least one positioning motor, is provided for operating the mains-disconnect relay, so that the article of furniture cannot be adjusted and/or the mains cannot be activated by operating a pushbutton switch alone. Increasing the protection against unintentional adjustment has the additional advantage that a different approach can be taken for designing the control unitxe2x80x94typically a manual switchxe2x80x94in that the safety features do no longer depend on the geometrical design of the manual switch.
Preferably, the switching device for operating the relay and the switching device for operating the at least one positioning motor are completely separated from each other galvanically when the mains is disconnected. This embodiment of the invention has the advantage that the drive unit, i.e., the positioning motors, cannot apply a sudden undesirable high load on the voltage source that supplies the control voltage or the control current, respectively, to the control contact of the relay for disconnecting the mains. If as in conventional devices, an auxiliary voltage source is used to power the control inputs of the mains-disconnect relay, i.e., a voltage source which provides a DC voltage to the pushbutton switch for operating the control input of the mains-disconnect relay that operates the positioning motor relay even after the mains has been disconnected, a brief high current surge (e.g., 100 ms duration at 3 A) can occur when the voltage source is as proposed connected in parallel, with the high current surge caused by the current drain of the positioning motors. This undesirable effect continues until the mechanical mains-disconnect relay switches with a predetermined time delay; as a result, the auxiliary voltage source (e.g., a battery) can be discharged unexpectedly fast and/or the other circuit components can experience undesirable current surges which in extreme cases can cause a malfunction.
Separating the switch that disconnects the mains from the pushbutton switches that operate the positioning motors of the drive assembly has additional advantages. One of the advantages is that the power disconnect circuit can be operated differently from the circuit that activates the positioning motors. While operating the positioning motors with pushbutton switches is convenient and easy, the mains should be disconnected from the mains only once before and after activation of the drive unit, in particular an unintentional activation should be reliably prevented. This could be accomplished by using a switch other than a pushbutton switch for disconnecting from the mains, for example, a slider switch with two defined switch positions, thereby almost entirely preventing an accidental activation of the switch.
According to another preferred embodiment of the invention, an inclination sensor is used instead of a slider switch, wherein the inclination sensor disconnects the mains automatically when a predetermined inclination angle is exceeded, for example in a situation where the mains power disconnect is located in the manual operating unit. In this case, the mains can be automatically disconnected when the manually operated control unit is picked up. Advantageously, the activation/disconnect positions can be adjusted on the manually operated control unit by a mechanical adjustment in order to take into consideration the different customer-specific rest positions of the control unit.
Alternatively, the switching device for activating the relay can also include an acoustic sensor. The acoustic sensorxe2x80x94and/or a processing unit connected thereafterxe2x80x94can for example be designed so that the mains can be switched on in response to a sound signal which produces on the sensor a predetermined audio level. This type of switching on the mains can particularly benefit disabled persons; even more advantageously, a solution incorporating a speech sensor for enabling/disconnecting the mains can be combined with a method for controlling the adjustment device of an article of furniture by speech input, as disclosed in DE 43 15 210 C2. It may also be possible to activate in a simple manner, in this case by a speech command, several functionsxe2x80x94i.e., enabling/disconnecting the mains and controlling the motor (the voice command causes, on one hand, the motor to be controlled and, on the other hand, the power mains to be connected), potentially even by using only a single command (xe2x80x9cUPxe2x80x9d, xe2x80x9cDOWNxe2x80x9d). Other hand, when mains are to be disconnected, the voice command can also completely galvanically separate the circuit section xe2x80x9cdrive unitxe2x80x9d from the switching section xe2x80x9cpower disconnect control.xe2x80x9d
Another advantageous embodiment of the invention employs a motion sensor as switching means for activating the relayxe2x80x94i.e., for disconnecting the mains. The mains can be disconnected by arranging the motion sensors in a suitable pattern, for example on a auxiliary table or, if desired, in a housing separate from the manual switch, and moving a hand past the sensor.
Alternatively, the switching device for operating the relay can also include a contact sensor, for example a sensor with a conductive plastic, or a capacitive contact sensor with a metal plate, whereby the electric field can be changed by placing a finger on the plate.
Advantageously, the control device for actuating the relay can also include a light-sensitive sensor. A light-sensitive sensor can be designed, for example, so that the mains is connected when the light level in a room exceeds the background illumination, for example, when a lamp is switched on or in daylight. In the dark, i.e., during sleep, the power mains remain disconnected.
The afore-described embodiments of the switch designs for disconnecting the mainsxe2x80x94as described abovexe2x80x94can be arranged in different locations of the circuit and the adjustment device. For example, for hospital beds, a patient could be allowed to operate the positioning motors, but may not be permitted to operate the power disconnect, for example, the patient""s body may have to remain in a certain position during the night. In such situations, the switch for disconnecting the mains should advantageously be placed separate from the control unit, for example in the drive unit, the mains plug assembly, in the power cord or at another suitable location (see the detailed description of the FIGS.). This provides a suitable interlock device for applications in hospitals.
Additional advantageous embodiments of the invention are described in the dependent claims.